Spatial Division Multiple Access (SDMA) is a method of multiplexing several signal streams, each one targeted to a different destination, simultaneously, by utilizing multiple transmit antennas. An SDMA channel access method may enable the use of the same frequency at the same time to communicate with several stations located in different places. For example, an SDMA Access Point (AP) having multiple antennas may use a beamforming technique to transmit to several remote stations (STAB), also referred to as users simultaneously. Each transmit antenna may transmit the intended signal multiplied by a certain weight, and by dynamically controlling the weights of each antenna the transmission may be directed to a desired location. In Multi-User Multiple-Input-Multiple-Output (MU MIMO) communication systems, a multi-antenna AP may transmit simultaneously to several multiple-antenna users, using SDMA technique.
Channel state information (CSI) may be estimated by an explicit sounding exchange. In explicit sounding exchange, the AP may send a sounding frame from which the intended user may estimate the CSI between the AP antennas and the user antennas. In sounding feedback, each user can return CSI. Using this information, the AP may design the transmit beamforming vectors that may assure good signal-to-interference-plus-noise ratio (SINR) for the data streams of users.
After designing the transmit beamforming vectors, the AP may estimate SINR of each stream of each user, and the obtained SINR values may be used for choosing transmission parameters such as data rate, modulation and coding scheme (MCS), bandwidth, number of spatial streams, etc for each user. In many applications it is desired that the AP will choose transmission parameters that will allow maximal data rate under required quality levels, typically given as maximal allowed packet error rate (PER).